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Infrared multiple photon dissociation spectra of proton- and sodium ion-bound glycine dimers in the N-H and O-H stretching region.

Authors
  • Atkins, Chad G
  • Rajabi, Khadijeh
  • Gillis, Elizabeth A L
  • Fridgen, Travis D
Type
Published Article
Journal
The Journal of Physical Chemistry A
Publisher
American Chemical Society
Publication Date
Oct 16, 2008
Volume
112
Issue
41
Pages
10220–10225
Identifiers
DOI: 10.1021/jp805514b
PMID: 18816028
Source
Medline
License
Unknown

Abstract

The proton- and the sodium ion-bound glycine homodimers are studied by a combination of infrared multiple photon dissociation (IRMPD) spectroscopy in the N-H and O-H stretching region and electronic structure calculations. For the proton-bound glycine dimer, in the region above 3100 cm (-1), the present spectrum agrees well with one recorded previously. The present work also reveals a weak, broad absorption spanning the region from 2650 to 3300 cm (-1). This feature is assigned to the strongly hydrogen-bonded and anharmonic N-H and O-H stretching modes. As well, the shared proton stretch is observed at 2440 cm (-1). The IRMPD spectra for the proton-bound glycine dimer confirms that the lowest energy structure is an ion-dipole complex between N-protonated glycine and the carboxyl group of the second glycine. This spectrum also helps to eliminate the existence of any of the higher-energy structures considered. The IRMPD spectrum for the sodium ion-bound dimer is a much simpler spectrum consisting of three bands assigned to the O-H stretch and the asymmetric and symmetric NH 2 stretching modes. The positions of these bands are very similar to those observed for the proton-bound glycine dimer. Numerous structures were considered and the experimental spectrum agrees with the B3LYP/6-31+G(d,p) predicted spectrum for the lowest energy structure, two bidentate glycine molecules bound to Na (+). Though some of the structures cannot be completely ruled out by comparing the experimental and theoretical spectra, they are energetically disfavored by at least 20 kJ mol (-1).

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